The onboard diagnostic systems on modern automobiles are a complex interaction between various computer algorithms and many different sensors. The onboard diagnostics II (OBDII) system has been required on all U.S. vehicles produced since 1996. Although the OBDII system provides a measure of standardization and commonality, the system expanded the scope of monitored components as well a provided specific performance criteria for determining malfunctions. These additional requirements have led to an increase in the amount of onboard sensors and algorithms.
When a sensor failure occurs, it must be comprehended and reported to the operator for remedial action. Various options exist to determine the health of a particular sensor. One option may be to employ a secondary or redundant sensor to rationalize the output of the primary sensor. Yet another option is to fully map the characteristics of the particular sensor under all conditions and populate a look up table (LUT) with these values. This approach is very application specific. A new map may be required for each model of vehicle and, depending on the sensor in question, possibly each engine or transmission variant. To reduce the size of the LUT, engineers and calibrators may limit the range in which the diagnostics will operate. They may employ strict enabling conditions to prevent false failure reporting. These strict enabling conditions may inhibit the diagnostic routine from functioning for a majority of the time.